This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A023992 #15 Jun 11 2025 09:14:50 %S A023992 3,7,9,11,11,15,15,19,18,19,21,24,22,25,26,28,26,29,29,34,33,34,36,38, %T A023992 35,38,38,39,38,41,42,44,43,44,46,49,45,50,50,52,51,54,55,58,55,56,58, %U A023992 61,57,60,60,61,60,63,62,66,64,66,67,71,68,70,72,73,70,72,70,76,74,75,77,79,76 %N A023992 Sum of exponents of primes in multinomial coefficient M(4n; n+2,2n,n-2). %H A023992 Amiram Eldar, <a href="/A023992/b023992.txt">Table of n, a(n) for n = 2..10000</a> %F A023992 a(n) = A022559(4*n) - A022559(2*n) - A022559(n+2) - A022559(n-2). - _Amiram Eldar_, Jun 11 2025 %t A023992 a[n_] := PrimeOmega[Multinomial[2*n, n+2, n-2]]; Array[a, 100] (* _Amiram Eldar_, Jun 11 2025 *) %o A023992 (PARI) a(n) = bigomega((4*n)! / ((2*n)!*(n-2)!*(n+2)!)); \\ _Amiram Eldar_, Jun 11 2025 %Y A023992 Cf. A001222, A022559. %Y A023992 Cf. A023978, A023979, A023980, A023981, A023982, A023983, A023984, A023985, A023986, A023987, A023990, A023991, A023993. %K A023992 nonn %O A023992 2,1 %A A023992 _Clark Kimberling_ %E A023992 Missing a(1)=1 inserted by _Sean A. Irvine_, Jun 17 2019 %E A023992 Offset changed to 2 and a(1) removed by _Amiram Eldar_, Jun 11 2025